Summary The Precision Helicopters Inc. Bell 206B Jet Ranger helicopter (registration C-GPGX, serial number1362) was departing from a prepared helicopter landing area adjacent to the Nose Mountain, Alberta, fire observation tower at approximately 1815mountain daylight time. A pilot and three initial attack firefighters were on board. The landing area was located in a clearing, on a mountain plateau, situated at the north edge of a steep escarpment. After lifting off, the pilot hover-taxied around a pile of brush on the west side of the clearing and departed in a westerly direction, toward the escarpment. When the helicopter overflew the rim of the escarpment, it began to yaw to the right. The pilot was unable to control the yaw with the application of full left pedal. As the helicopter rotated through 180, the pilot lowered the collective to regain directional control. The helicopter descended onto the escarpment, rolled over, and came to rest on its left side. One firefighter sustained fatal injuries and another firefighter sustained serious injuries. The pilot and the third firefighter sustained minor injuries. The impact forces activated the onboard emergency locator transmitter. The helicopter was substantially damaged, but there was no post-impact fire. Ce rapport est galement disponible en franais. Other Factual Information Precision Helicopters Inc. operates two Eurocopter AS350 helicopters and one Bell206B helicopter under the sections702 and 703of the Canadian Aviation Regulations (CARs). The helicopter had been chartered by the Alberta Ministry of Sustainable Resource Development Forest Protection Branch (ASRD-FPB). It had been dispatched with the pilot and the three-member initial attack firefighting crew from the Graham Fire Base at 1614mountain daylight time.1 There had been widespread thunderstorm and lightning activity in the area, and the crew was tasked to investigate reports of forest fires burning to the south of Nose Mountain. After encountering thunder cells and strong downdrafts en route to the fires, the pilot diverted to Nose Mountain to take on fuel. Another thunderstorm moving through the Nose Mountain area forced the pilot to land six miles south of Nose Mountain to allow time for the weather to pass. The helicopter arrived at the Nose Mountain landing area at 1803where it was shut down and the firefighters deplaned. Approximately 22USgallons of JetA fuel was added, bringing the indicated total fuel on board to 45USgallons. Following refuelling, the pilot and the same three firefighters boarded the helicopter and departed on the accident flight. Weather Visual meteorological conditions prevailed at Nose Mountain at the time of the accident. However, there was widespread thunderstorm and lightning activity in the area. Hourly winds and temperatures are not formally recorded at the site. Temperature estimates from personnel at the site ranged from 15C to 28C. Using a figure of 22C, the density altitude would have been approximately 7000feet. The winds were shifting from the northeast to the southeast at speeds estimated up to 10knots. Landing Area The landing area measured about 200by 150feet and was on the northeast side of a clearing, surrounded on three sides by trees up to 25feet tall. Second growth brush had recently been removed from the clearing to improve aircraft operations and facilitate multiple helicopter landings and departures. A mound of brush about 6feet high and 20feet in diameter had been piled in the clearing, to the west of the landing area. The distance from the landing area to the escarpment was about 200feet, and the distance from the take-off position to the rim of the escarpment was about 125feet (see AppendixA). The elevation of the landing area is 4879feet above sea level(asl). The prevailing winds were normally from the west, and pilots usually departed from the landing area to the west and over the escarpment. A departure directly to the east would have required an initial climb of 25to 30feet to clear the tree-line. The pilot had departed directly from the landing area toward the escarpment many times in the past, often at high gross weight. To depart toward the escarpment on the accident flight, it was necessary to manoeuvre the helicopter to avoid the brush pile. The pilot performed a clearing hover turn to the right, then hover-taxied southward, while maintaining a westerly heading, along the southeast edge of the clearing. This positioned the helicopter for an unobstructed take-off run to the west, across flat ground and toward the escarpment. The helicopter did not attain sufficient speed for translation lift2 before reaching the rim of the escarpment. The accident site is at latitude 5434'N, longitude 11938'W. Pilot The pilot was certified and qualified for the flight in accordance with existing regulations. He held a valid Canadian commercial helicopter pilot licence and a valid aircraft maintenance engineer (AME) licence. He had accumulated about 5250hours of total flying experience, of which about 3750hours were on Bell206 helicopters. He had worked for Precision Helicopters Inc. since 1981and had performed flying duties since 1986. At the time of the accident, he was the company Chief Pilot and the Operations Manager. He met all company recurrent ground and flight training requirements and was knowledgeable of the conditions that can contribute to insufficient power situations and unanticipated right yaw in Bell helicopters. The pilot had used the Nose Mountain landing area several hundred times during the 20years he had been flying in the area and five or six times in2006. The pilot was well rested before commencing his duty day at 1030in the morning, and there was no indication that physiological factors had affected his performance. He was characterized by clients and peers as being an extremely competent and cautious pilot. Helicopter There was no indication of any pre-existing flight control or tail rotor drive system malfunction that would have contributed to the accident. The engine (Rolls-Royce 250C20) had been modified with the installation of a Rolls-Royce 250-C20B compressor and turbine, under the provisions of an approved Allison Commercial Engine Bulletin. The effect of this modification was to provide improved high-altitude performance. The helicopter was fitted with a particle separator. Helicopter Weight and Balance The pilot had estimated the weight of the firefighters and their gear before departing the Graham fire base. This practice was the norm for the helicopter pilots engaged in firefighting activities. On the weight and balance report provided to TSB investigators by the pilot, the firefighter weights were recorded as 200,150, and 130pounds, and the baggage weight was recorded as 100pounds. As a result, the gross weight at take-off was calculated as 3104pounds. The maximum take-off weight for a Bell206B helicopter with an internal load is 3200pounds. All of the gear and equipment on the helicopter was subsequently recovered and weighed on a calibrated scale. The total weight of the gear and equipment was 239pounds. It was estimated that each passenger was wearing an additional 14to 17pounds of personal firefighting gear and safety equipment that was not included in the original passenger weight estimates. Post-accident weight and balance calculations using the revised gear and passenger weights indicated that the weight at take-off was approximately 3245pounds. Passenger Weighing Practices Section 703.37 of the CARs requires air operators to have a weight and balance system that meets the Commercial Air Service Standards (CASS). CASS Section 723.37describes three methods to determine the weight of passengers: by actual weight, by using approved standard weights, or by using approved survey weights. Cargo weight must be actual weight. The Precision Helicopters Inc. operations manual required actual weights to be used for computing the load when the pilot-in-command estimates the passenger weights to be more or less than the published standard weights. As indicated above, the pilot had estimated the weight of passengers and gear on board the helicopter. ASRD-FPB provides The Pilot's Handbook to pilots working on fire management programs in Alberta. The handbook imparts basic information on ASRD-FPB policy and procedures. AppendixB of the handbook outlines the pilot and government representative responsibilities for rotary-wing load calculations. It states that the pilot is responsible for computing the allowable payload on a helicopter; however, a government representative is responsible for providing an accurate passenger/cargo manifest and weights. At the time of the accident, ASRD-FPB had no formal system in place to provide helicopter pilots with actual individual firefighter weights, including personal gear. As well, there was no information available to firefighters to indicate that excess weight was a critical issue on the smaller helicopters used by ASRD-FPB. Firefighters employed by ASRD-FPB undergo fitness testing annually in the spring. At that time, they weigh themselves and record their own weight. This self-weighing procedure forms part of the ASRD-FPB weight-monitoring system. Not included in that recorded weight is the extra gear firefighters are required to wear or have on them while flying in a helicopter: boots; hard hat; coveralls; gloves; a safety belt containing a first-aid kit and water bottle; and in the case of a team leader, one or two hand-held radios. In recent years, ASRD-FPB had preferred to transport initial attack crews in helicopters capable of carrying larger loads, such as the Eurocopter AS350. ASRD-FPB continued to use Bell206B helicopters during periods when helicopters were in high demand, such as when firefighting activities were being carried out. The initial attack crews were familiar with the higher load carrying capacity of the AS350helicopter. Engine Power Available For helicopters, engine power available is a term commonly used to refer to the differential between the power being used and the limits of the engine performance, namely, power turbine speed, temperature, and torque. Increases to density altitude or aircraft weight and hover flight in tailwind conditions all result in an increase in the power required to hover. In turn, this reduces the margin of engine power available and affects the overall take-off performance. In a light helicopter, such as the Bell206, seemingly insignificant weight additions can affect the power required to hover. The maximum permitted take-off torque for the engine installed on the accident helicopter is 100percent for five minutes, with a transient over-torque of 110percent permitted for five seconds. Before the commencement of forward flight from the departure point in the clearing, the torque required to hover in ground effect was 96percent; it is probable that this value increased slightly during the initial transition out of the stationary hover. The usual torque indications for Bell206B helicopters hovering in ground effect and in similar load and conditions are reported to be in the order of 85to 90percent. The helicopter did not attain the benefits from translational lift before reaching the rim of the escarpment, where the performance benefit of ground effect was lost. Considering the helicopter weight and the density altitude, an increase in power above 96percent would have been required to maintain level flight once the helicopter cleared the rim of the escarpment. Unanticipated Right Yaw The adverse phenomenon of unanticipated right yaw (URY) is highly publicized in training and other aviation literature.3, 4, 5, 6 The information contained in these documents is reproduced in a Federal Aviation Administration (FAA) publication titled The Rotorcraft Flying Handbook, which states the following: In general, URY may occur when a helicopter is operating at low speed and high power in a tailwind, especially at higher altitudes, where the air is thinner and tail rotor thrust and efficiency are reduced. The initial pilot response to correct this condition is to lower the collective lever. This reduces the torque produced by the main rotor, reduces the anti-torque thrust requirement of the tail rotor, and increases its efficiency. Even though helicopter pilots are aware of the URY phenomenon, several occurrences in the past have shown that pilots did not recognize the potential for URYbefore experiencing the loss of control. It was not determined if the occurrence pilot had recognized that the existing wind, density altitude, and terrain conditions created the potential for URYto occur during the accident take-off and departure. Hover Performance The hover out-of-ground effect (HOGE) charts in the Bell206B Flight Manual provide hover performance (that is, maximum allowable gross weight) for conditions of pressure altitude and temperature. The charts are divided into AreaA and AreaB. AreaA indicates hover performance for which satisfactory stability and control has been demonstrated in relative winds of 17knots sideward and rearward for all loading conditions. AreaB indicates hover performance that can be realized in calm winds or in winds outside the critical relative wind azimuth area. Tail rotor control may not be possible for operations in AreaB of the hover ceiling charts when the relative wind is in the critical wind azimuth area. For the Bell206B, the critical relative wind azimuth area extends clockwise 50 from the nose of the helicopter to 210 from the nose of the helicopter (see AppendixB). The Bell 206B HOGE chart indicates that, for the conditions at the occurrence site, 2925pounds would be the maximum weight to HOGE and remain in AreaA (see AppendixC). At 3245pounds, the helicopter was about 320pounds above that maximum weight, and now in AreaB of the HOGEchart. Crashworthiness/Survivability The firefighter in the left cockpit seat was seriously injured by the main rotor when the main rotor penetrated the cabin following impact with the terrain. The firefighter in the left cabin seat was fatally injured, likely due to a combination of the same main rotor strike and ground impact forces. Rescue and medical information indicated that this firefighter was likely wearing only the lap-belt and not wearing the available shoulder harness portion of the seat restraint. Two-bladed teetering rotor systems are inherently unstable at low rpm compared to multi-bladed rigid rotor systems, and information from similar accidents indicates that helicopters with two-bladed main rotor blade systems demonstrate a higher rate of injury caused by the rotor blades penetrating the cabin than do helicopters with multiple main rotor blade systems. The fire tower attendant initiated rescue efforts via the forestry radio network, and two helicopters were diverted to the accident site. The pilot, fire-tower attendant, and arriving forestry personnel performed emergency first aid at the site. The occupants of the occurrence helicopter were transported by helicopter to Grande Prairie, Alberta.